1. Field of the Invention
The invention relates to an orthodontic bracket system, more particularly, to a self ligating bracket that may include a shape memory sliding clip.
2. Brief Description of Related Art
Orthodontic treatment typically involves dental work intended to correct irregularities of the teeth or of the relation of the teeth to surrounding anatomy. The irregularities may involve malocclusions with varying degrees of severity. Examples of malocclusions include, spacing irregularities, such as excessive crowding or diastema, overbite irregularities, and underbite irregularities. Treatment of the listed exemplary irregularities, as well as others, typically involves installing braces or mechanical aids needed to reposition the teeth into an appropriate or correct orthodontic alignment.
Braces conventionally include orthodontic brackets designed to be attached to either the labial or lingual surface of a tooth. The brackets generally include archwire slots within which a flexible, yet resilient, archwire is positioned. Each bracket is affixed to the appropriate tooth surface so that the archwire slot is oriented to facilitate the archwire being positioned therein. The brackets can be oriented in a variety of ways wherein the archwire extends orthogonally or parallel relative to the long axis of the root of the tooth.
Since Dr. Edward Hartley Angle patented the Edgewise bracket in the 1920's, the biomechanical function of orthodontic brackets remains essentially unchanged. Despite significant improvements in design, state of the art manufacturing processes, and the development of new materials since the Edgewise bracket was patented, the concept of moving and having control of teeth in three dimensions remains the same. The quality and development of new materials associated with low force biological concepts has provided orthodontists with a new approach to preserving periodontal ligament integrity during the treatment of malocclusions.
The geometric configuration of the bracket incorporates an archwire slot oriented horizontally, transverse relative to the face of the bracket, with a pair of parallel walls arranged substantially perpendicular to the slot floor, which define a rectangular slot configuration in the cross section. The parallel walls are conventionally referred to as tie wings or extensions which project upwardly and away from the tooth surface.
An archwire is positioned within the archwire slot and may have varied dimensions and cross sections (e.g., round, rectangular, etc.) from which an orthodontic professional may select based on the intended use and/or need of the patient. Moreover, the configuration of the archwire may be selected based on the phase of treatment and the extent the teeth need to move during the treatment plan established by the orthodontist. For example, the archwire is known to be manufactured from metal, a metallic material, and/or a shape memory material and which can be bent or twisted prior to being inserted within the archwire slot. The memory or restorative force exerted by the archwire onto the brackets helps move the teeth to the desired alignment.
Orthodontic brackets have different features, determined statistically for values like torque, angulation, in and out, offsets, extrusions inherent to the positioning of the arch slot on a tooth by tooth basis, all of which give the orthodontist the option to individualize the set of brackets to be used in the treatment according to the facial pattern and the ideal positioning of the tooth for angulation and inclination, thereby minimizing the need for bends and adjustments on the archwires. In orthodontics, this treatment methodology is conventionally known as “Straight Wire Appliance,” conception of which took place in the 1970s and is commonly attributed to Dr. Lawrence Andrews.
In the 1930s, self ligating brackets became commercially available. The primary characteristic of such brackets in the 1930s was the ease with which an archwire could be changed, which saved orthodontists significant hours of chair time. In the 1970's, numerous studies and research of friction in the archwire slot spawned a new generation of self ligating brackets which were based on the concept of low friction and sliding mechanics. Consequently, an approach was developed wherein low friction mechanics and forces were used to move teeth with ligatureless orthodontic brackets.
The use of steel ligatures or elastomeric ligatures associated with conventional brackets presents new difficulties and concerns. For example, the placement of steel ligatures is a time consuming operation that can lead to motion repetitive injuries to the orthodontic professional. Moreover, there are considerable costs associated with the specific procedures required when using the set of sterilized instruments that are dedicated to the placement of the bracket on the tooth. Also, elastomeric ties, although easier to place around the bracket than the previously used ties, deteriorate fairly rapidly within the mouth of the patient, absorb water, and accumulate excess plaque, thereby leading to an undesirable condition of the periodontum, such as inflammation. Both ligating methods, i.e., the methods which use steel ligatures and elastomeric ties, suffer from the concern of high friction forces being applied to the binary bracket/archwire once normal forces are applied, which press the archwires against the bottom of the slot and prevent the working energy that is carried by the archwire from being applied to the tooth movement. The restrictive force, independent of the treatment methodology or technique used, results in an increase in the frequency in which the archwire must be changed, as well as higher force levels being applied from the archwire to the bracket.
In the 80's, the above-mentioned low friction/low force concept gained momentum with the development of new alloys that were used in the manufacture of the archwires. The alloys were developed to have a low force modulus tailored to the force needs of the self ligating brackets. The reduced friction permitted the teeth to slide more easily during certain stages of the treatment with the low force modulus contributing to faster treatments that required less visits to the orthodontist and less pain experienced by the patient.
A difficult task in choosing the archwire that is used to move teeth is the predictability of the effective force that will be delivered by the archwire to the teeth. Restrictive forces from steel ligatures or elastomeric O-rings are variables that lead to indeterminate effective forces being used in tooth movement. Also, sometimes, the steel and elastomeric ligatures bend the archwires beyond their elastic properties, resulting in notching of the wire or plastically deforming the wire in a manner that results in a permanent bend.
Research of the self ligating bracket using state of the art force testing equipment determined that 6% to 10% of the applied force is lost due to friction. Therefore, 90% of the applied force becomes effective force used to move teeth.
Although reduced friction is desirable, there are occasions when more friction is desired, such as towards the end of the treatment plan when consolidation of the arch form in three planes is needed to stabilize the achieved result and the dental arch form. Clinical modifications or placement of more conventional brackets becomes a requirement as treatment proceeds, resulting in an increase in material cost and time consuming procedures in the office.
Further, self ligating brackets include moving parts that become distorted, warped or disengaged, thereby compromising the pace of treatment.
To date, several self-locking or self-ligating (ligatureless) orthodontic brackets have been designed. However, most brackets have complex designs, and/or incorporate features that require prohibitively expensive machining operations or include a plurality of separate parts, which in turn increases the number of failure modes for such brackets. The complexity in design and manufacturing processes for orthodontic self ligating brackets has driven prices exceedingly above the costs of a conventional bracket and without providing the option of converting the bracket when needed or replacing the clip in the event of breakage or malfunctioning.
Thus, there is a need for a self ligating orthodontic bracket to overcome the deficiencies and drawbacks of conventional self ligating brackets available today.